WATCH: "Captain America: Civil War" Featurette Touts 'Much Darker Version' of Iron Man

"Captain America: Civil War" hits theaters in a month, and -- in a new behind-the-scenes featurette by Good Morning America -- the cast and crew promise there are plenty of surprises in store for fans of the Marvel Cinematic Universe.

"It's not going to be entirely predictable. Characters are going to make choices that surprise you," Robert Downey Jr. teased.

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"I think that Marvel likes to keep the fans excited and guessing and curious," added Scarlett Johanssen.

"Downey is playing a much darker version of Tony Stark than he's ever played," shared director Joe Russo, "And he's just crushing it."

As to the source material itself, Chris Evans said, "The comic books were really wonderful pieces of literature."

Directed by Joe and Anthony Russo and starring Chris Evans, Robert Downey Jr., Scarlett Johansson, Anthony Mackie, Sebastian Stan and more, "Captain America: Civil War" opens on May 6, 2016.

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